Camera accessory, camera body and camera system

ABSTRACT

A camera accessory is detachably mounted at a camera body that includes a first body contact point, a second body contact point, a third body contact point, a fourth body contact point and a fifth body contact point and detects disengagement of the camera accessory when the fifth body contact point sustains a signal level corresponding to a first truth value continuously over a length of time equal to or greater than a predetermined time length. In the camera accessory, the accessory-side communication control device executes control so as to ensure that the signal assuming a level corresponding to the first truth value is not continuously output from the fifth accessory contact point any longer than the predetermined time length while the operating voltage supply from the camera body is provided via the first accessory contact point.

This is a Continuation of application Ser. No. 13/944,449 filed Jul. 17,2013, which in turn is a Continuation of application Ser. No. 13/687,083filed Nov. 28, 2012, which in turn is a Continuation of application Ser.No. 13/403,427 filed Feb. 23, 2012, which claims the benefit of U.S.Provisional Application No. 61/554,672 filed Nov. 2, 2011. Thisapplication also claims priority from Japanese Patent Application No.2011-039430 filed Feb. 25, 2011, and Japanese Patent Application No.2011-189736 filed Aug. 31, 2011. The disclosures of each of the earlierapplications are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a camera accessory, a camera body and acamera system.

2. Description of Related Art

A camera system known in the related art may include contact points toenable communication between the camera body and an exchangeable lens(photographic lens). In such a camera system, engagement/disengagementof the exchangeable lens may be detected via the communication contactpoints. For instance, Japanese Laid Open Patent Publication No. H8-95144discloses a camera system that detects engagement of a photographic lensbarrel via a communication line BINTL between the photographic lensbarrel and the camera body. Since the communication line BINTL isutilized both for inputting data to the camera body and for outputtingdata from the camera body, a BCPU inside the camera body needs to switcha terminal of the communication line so as to allow the terminal tofunction as an input terminal when detecting photographic lens barrelengagement/disengagement and to switch the same terminal so as to allowit to function as an output terminal when conducting communication.

SUMMARY OF THE INVENTION

There is an issue with the engagement/disengagement detection mechanismdisclosed in the publication in that its structure is bound to becomplicated.

A camera accessory to be detachably mounted at a camera body thatincludes a first body contact point, a second body contact point, athird body contact point, a fourth body contact point and a fifth bodycontact point and detects disengagement of the camera accessory when thefifth body contact point sustains a signal level corresponding to afirst truth value continuously over a length of time equal to or greaterthan a predetermined time length, according to a first aspect of thepresent invention, the camera accessory comprises: a mounting device tobe detachably mounted at the camera body; a first accessory contactpoint that is connected with the first body contact point while thecamera accessory is engaged with the camera body so as to receive anoperating voltage supplied from the camera body; a second accessorycontact point that is connected with the second body contact point whilethe camera accessory is engaged with the camera body so as to allow aclock signal output from the camera body to be input thereat; a thirdaccessory contact point that is connected with the third body contactpoint while the camera accessory is engaged with the camera body so asto allow a first data signal output from the camera body to be inputthereat; a fourth accessory contact point that is connected with thefourth body contact point while the camera accessory is engaged with thecamera body so as to allow a second data signal to be output to thecamera body; a fifth accessory contact point that is connected with thefifth body contact point while the camera accessory is engaged with thecamera body so as to allow a signal assuming a level corresponding tothe first truth value to be output to the camera body during a timeperiod in which input operation for the first data signal via the thirdaccessory contact point and output operation for the second data signalvia the fourth accessory contact point are disallowed; and anaccessory-side communication control device that executes the inputoperation for the first data signal from the camera body via the thirdaccessory contact point and the output operation for the second datasignal to output the second data signal to the camera body via thefourth accessory contact point in synchronization with the clock signalinput at the second accessory contact point, wherein: the accessory-sidecommunication control device executes control so as to ensure that thesignal assuming a level corresponding to the first truth value is notcontinuously output from the fifth accessory contact point any longerthan the predetermined time length while the operating voltage supplyfrom the camera body is provided via the first accessory contact point.

A camera accessory to be detachably mounted at a camera body thatincludes a first body contact point, a second body contact point, athird body contact point, a fourth body contact point and a fifth bodycontact point and detects disengagement of the camera accessory when thefifth body contact point sustains a signal level corresponding to afirst truth value continuously over a length of time equal to or greaterthan a predetermined time length, according to a second aspect of thepresent invention, the camera accessory comprises: a mounting device tobe detachably mounted at the camera body; a first accessory contactpoint that is connected with the first body contact point while thecamera accessory is engaged with the camera body so as to receive anoperating voltage supplied from the camera body; a second accessorycontact point that is connected with the second body contact point whilethe camera accessory is engaged with the camera body so as to allow aclock signal output from the camera body to be input thereat; a thirdaccessory contact point that is connected with the third body contactpoint while the camera accessory is engaged with the camera body so asto allow a first data signal output from the camera body to be inputthereat; a fourth accessory contact point that is connected with thefourth body contact point while the camera accessory is engaged with thecamera body so as to allow a second data signal to be output to thecamera body; a fifth accessory contact point that is connected with thefifth body contact point while the camera accessory is engaged with thecamera body so as to allow a signal assuming a level corresponding tothe first truth value to be output to the camera body during a timeperiod in which input operation for the first data signal via the thirdaccessory contact point and output operation for the second data signalvia the fourth accessory contact point are disallowed; and anaccessory-side communication control device that executes the inputoperation for the first data signal from the camera body via the thirdaccessory contact point and the output operation for the second datasignal to output the second data signal to the camera body via thefourth accessory contact point in synchronization with the clock signalinput at the second accessory contact point, wherein: the accessory-sidecommunication control device executes control so that a signal, whichdisallows detection of disengagement of the camera accessory from thecamera body, is output from the fifth accessory contact point while theoperating voltage supply from the camera body is provided via the firstaccessory contact point.

A camera accessory to be detachably mounted at a camera body thatincludes a first body contact point, a second body contact point, athird body contact point, a fourth body contact point and a fifth bodycontact point and detects disengagement of the camera accessory when thefifth body contact point sustains a signal level corresponding to afirst truth value continuously over a length of time equal to or greaterthan a predetermined time length, according to a third aspect of thepresent invention, the camera accessory comprises: a mounting device tobe detachably mounted at the camera body; a first accessory contactpoint that is connected with the first body contact point while thecamera accessory is engaged with the camera body so as to receive anoperating voltage supplied from the camera body; a second accessorycontact point that is connected with the second body contact point whilethe camera accessory is engaged with the camera body so as to allow aclock signal output from the camera body to be input thereat; a thirdaccessory contact point that is connected with the third body contactpoint while the camera accessory is engaged with the camera body so asto allow a first data signal output from the camera body to be inputthereat; a fourth accessory contact point that is connected with thefourth body contact point while the camera accessory is engaged with thecamera body so as to allow a second data signal to be output to thecamera body; a fifth accessory contact point that is connected with thefifth body contact point while the camera accessory is engaged with thecamera body so as to allow a signal assuming a level corresponding tothe first truth value to be output to the camera body during a timeperiod in which input operation for the first data signal via the thirdaccessory contact point and output operation for the second data signalvia the fourth accessory contact point are disallowed; and anaccessory-side communication control device that executes the inputoperation for the first data signal from the camera body via the thirdaccessory contact point and the output operation for the second datasignal to output the second data signal to the camera body via thefourth accessory contact point in synchronization with the clock signalinput at the second accessory contact point, wherein: the accessory-sidecommunication control device controls an output from the fifth accessorycontact point so as to ensure that the camera body does not detectdisengagement of the camera accessory from the camera body while theoperating voltage supply from the camera body is provided via the firstaccessory contact point.

According to a fourth aspect of the present invention, in the cameraaccessory according to any one of the first to third aspects, it ispreferable that the accessory-side communication control device outputsa signal assuming a level corresponding to a second truth valuedifferent from the first truth value via the fifth accessory contactpoint while the operating voltage supply from the camera body isprovided via the first accessory contact point and the accessory-sidecommunication control device executes the input operation for the firstdata signal and the output operation for the second data signal.

According to a fifth aspect of the present invention, in the cameraaccessory according to any one of the first to fourth aspects, it ispreferable that the accessory-side communication control device controlssignal levels at the second through fifth accessory contact points so asto ensure that the fifth accessory contact point, among the secondthrough fifth accessory contact points, undergoes fewest signal levelshifts during the input operation for the first data signal or theoutput operation for the second data signal.

According to a sixth aspect of the present invention, the cameraaccessory according to the fifth aspect may further comprises fouradditional accessory contact points each connected with one of four bodycontact points used for a communication operation different from theinput operation for the first data signal or the output operation forthe second data signal, which are different from the first through fifthbody contact points at the camera body, wherein: the accessory-sidecommunication control device controls signal levels at the secondthrough fifth accessory contact points and the four additional accessorycontact points so as to ensure that the fifth accessory contact point,among the second through fifth accessory contact points and the fouradditional accessory contact points, undergoes fewest signal levelshifts.

According to a seventh aspect of the present invention, in the cameraaccessory according to any one of the first to sixth aspects, the fifthaccessory contact point may be grounded via a pull-down resistor insidethe camera accessory.

A camera body according to an eighth aspect of the present inventioncomprises: a mounting device at which a camera accessory that includes afirst accessory contact point, a second accessory contact point, a thirdaccessory contact point, a fourth accessory contact point and a fifthaccessory contact point is detachably mounted; a first body contactpoint that is connected with the first accessory contact point while thecamera body is engaged with the camera accessory so as to provide anoperating voltage supply to the camera accessory; a second body contactpoint that is connected with the second accessory contact point whilethe camera body is engaged with the camera accessory so as to allow aclock signal to be output to the camera accessory; a third body contactpoint that is connected with the third accessory contact point while thecamera body is engaged with the camera accessory so as to allow a firstdata signal to be output to the camera accessory; a fourth body contactpoint that is connected with the fourth accessory contact point to allowa second data signal from the camera accessory to be input thereat whenthe camera body is engaged with the camera accessory; a fifth bodycontact point that is connected with the fifth accessory contact pointwhile the camera body is engaged with the camera accessory so as toallow a signal assuming a level corresponding to a first truth value tobe input thereat from the camera accessory during a time period in whichoutput operation for the first data signal via the third body contactpoint and input operation for the second data signal via the fourth bodycontact point are disallowed; a body-side communication control devicethat outputs the clock signal from the second body contact point andexecutes the output operation for the first data signal to output thefirst data signal to the camera accessory via the third body contactpoint and the input operation for the second data signal to input thesecond data signal from the camera accessory via the fourth body contactpoint in synchronization with the clock signal; and anengagement/disengagement detection device that detects disengagement ofthe camera accessory when the fifth body contact point sustains a signallevel corresponding to the first truth value continuously over a lengthof time equal to or greater than a predetermined time length, wherein:the body-side communication control device receives, via the fifth bodycontact point, a signal that does not sustain the signal levelcorresponding to the first truth value continuously over a length oftime equal to or greater than the predetermined length of time when thecamera accessory is mounted at the mounting device.

According to a ninth aspect of the present invention, in the camera bodyaccording to the eighth aspect, it is preferable that the body-sidecommunication control device receives, via the fifth body contact point,a signal assuming a signal level corresponding to a second truth valuedifferent from the first truth value while the output operation for thefirst data signal or the input operation for the second data signal isexecuted by the body-side communication control device, and receives asignal, via the fifth body contact point, assuming a signal levelcorresponding to the first truth value while the output operation forthe first data signal or the input operation for the second data signalis not in progress.

According to a tenth aspect of the present invention, in the camera bodyaccording to the eighth or ninth aspect, it is preferable that thebody-side communication control device receives, via the fifth bodycontact point, a signal undergoing fewest signal level shifts amongsignals exchanged via the second through fifth body contact pointsduring the output operation for the first data signal or the inputoperation for the second data signal.

According to an eleventh aspect of the present invention, the camerabody according to the tenth aspect may further comprises: fouradditional body contact points used for a communication operationdifferent from the output operation for the first data signal or theinput operation for the second data signal, which are each connectedwith one of four accessory contact points at the camera accessory andare different from the first through fifth body contact points, wherein:the body-side communication control device receives, via the fifth bodycontact point, a signal undergoing fewest signal level shifts amongsignals exchanged via the second through fifth body contact points andthe four additional body contact points during the output operation forthe first data signal or the input operation for the second data signal.

A camera system according to a twelfth aspect comprises: a camera body;and an accessory to be detachably mounted at the camera body, wherein:the camera body comprises: a first body contact point via which anoperating voltage supply to the accessory is provided; a second bodycontact point via which a clock signal is output to the accessory; athird body contact point via which a first data signal is output to theaccessory; a fourth body contact point via which a second data signalfrom the accessory is input; a fifth body contact point via which asignal from the accessory and assuming a level corresponding to a firsttruth value is input during a time period in which output operation forthe first data signal via the third body contact point and inputoperation for the second data signal via the fourth body contact pointare disallowed; a body-side communication control device that outputsthe clock signal from the second body contact point and executes theoutput operation for the first data signal to output the first datasignal to the accessory via the third body contact point and the inputoperation for the second data signal to input the second data signalfrom the accessory via the fourth body contact point in synchronizationwith the clock signal; and an engagement/disengagement detection devicethat detects disengagement of the accessory when the fifth body contactpoint sustains a signal level corresponding to the first truth valuecontinuously over a length of time equal to or greater than apredetermined time length; and the accessory comprises: a firstaccessory contact point that is connected with the first body contactpoint; a second accessory contact point that is connected with thesecond body contact point; a third accessory contact point that isconnected with the third body contact point; a fourth accessory contactpoint that is connected with the fourth body contact point; a fifthaccessory contact point that is connected with the fifth body contactpoint; and an accessory-side communication control device that executesthe input operation for first data signal to input the first data signalfrom the camera body via the third accessory contact point and theoutput operation for the second data signal to output the second datasignal to the camera body via the fourth accessory contact point insynchronization with the clock signal input at the second accessorycontact point; and the accessory-side communication control deviceexecutes control so as to ensure that the signal assuming a levelcorresponding to the first truth value is not continuously output fromthe fifth accessory contact point any longer than the predetermined timelength while the operating voltage supply from the camera body isprovided via the first accessory contact point.

According to a thirteenth aspect of the present invention, in the camerasystem according to the twelfth aspect of the present invention, it ispreferable that the accessory-side communication control device outputsa signal assuming a level corresponding to a second truth valuedifferent from the first truth value via the fifth accessory contactpoint while the operating voltage supply from the camera body isprovided via the first accessory contact point and the accessory-sidecommunication control device executes the input operation for the firstdata signal and the output operation for the second data signal, whereasthe accessory-side communication control device outputs via the fifthaccessory contact point, a signal assuming a signal level correspondingto the first truth value while the input operation for the first datasignal or the output operation for the second data signal is not inprogress.

According to a fourteenth aspect of the present invention, in the camerasystem according to the twelfth or thirteenth aspect, it is preferablethat the accessory-side communication control device controls signallevels at the second through fifth accessory contact points so as toensure that the fifth accessory contact point, among the second throughfifth accessory contact points, undergoes fewest signal level shiftsduring the input operation for the first data signal or the outputoperation for the second data signal.

According to a fifteenth aspect of the present invention, in the camerasystem according to the fourteenth aspect, it is preferable that thecamera body further comprises four additional body contact points usedfor a communication operation different from the output operation forthe first data signal or the input operation for the second data signal,which are different from the first through fifth body contact points;the accessory further comprises four additional accessory contact pointseach connected with one of the four additional body contact points; andthe accessory-side communication control device controls signal levelsat the second through fifth accessory contact points and the fouradditional accessory contact points so as to ensure that the fifthaccessory contact point, among the second through fifth accessorycontact points and the four additional accessory contact pointsundergoes fewest signal level shifts.

According to a sixteenth aspect of the present invention, in the camerasystem according to any one of the twelfth to fifteenth aspect, thefifth accessory contact point may be grounded via a pull-down resistorinside the accessory.

According to a seventeenth aspect of the present invention, in thecamera accessory according to any one of the first to seventh aspect,the camera accessory may be an exchangeable lens detachably mounted atthe camera body.

According to an eighteenth aspect of the present invention, in thecamera accessory according to any one of the first to seventh aspect,the camera accessory may be a middle accessory that includes two mountportions; and the camera body may be detachably mounted at one mountportion among the two mount portions and an exchangeable lens, whichcannot be mounted directly at the camera body, may be detachably mountedat another mount portion among the two mount portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of a camera system used in conjunction withexchangeable lenses, achieved in an embodiment of the present invention.

FIG. 2 is a sectional view of the camera system used in conjunction withexchangeable lenses, achieved in the embodiment of the presentinvention.

FIG. 3 is a schematic diagram pertaining to structural details ofholding portions.

FIG. 4 is a timing chart indicating a specific example of timing withwhich command data communication may be executed.

FIGS. 5A and 5B each present timing charts indicating a specific exampleof timing with which hot line communication may be executed.

FIGS. 6A and 6B present timing charts indicating how a lensengagement/disengagement detection unit may detectengagement/disengagement of an exchangeable lens.

FIG. 7 is a perspective of a camera system used in injunction withexchangeable lenses, which includes a middle adapter, achieved inanother embodiment of the present invention.

FIG. 8 is a perspective of a camera system used in injunction withexchangeable lenses, which includes a middle adapter, achieved in yetanother embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

FIG. 1 is a perspective of a camera system used in conjunction withexchangeable lenses, achieved in the first embodiment of the presentinvention. It is to be noted that FIG. 1 shows components pertaining tothe present invention only, and that illustrations and descriptions ofcomponents not directly related to the present invention are notprovided. A camera system 1 comprises a camera body 100 and anexchangeable lens (interchangeable lens, or photographic lens) 200 thatcan be detachably mounted at the camera body 100.

A body-side mount unit 101, at which the exchangeable lens 200 isdetachably mounted, is disposed at the camera body 100. A portion thatprojects out along part of the inner circumference of the body-sidemount unit 101 is provided at a position near the body-side mount unit101 (on the inner circumferential side of the body-side mount unit 101)at the camera body 100 so as to be used as a holding portion (electricalconnection portion) 102 that holds contact points. A plurality ofcontact points are disposed at the holding portion 102.

In addition, the exchangeable lens 200 includes a lens-side mount unit201, corresponding to the body-side mount unit 101, to which the camerabody 100 can be detachably mounted. A portion that projects out alongpart of the inner circumference of the lens-side mount unit 201 isprovided at a position near the lens-side mount unit 201 (on the innercircumferential side of the lens-side mount unit 201) at theexchangeable lens 200 so as to be used as a holding portion (electricalconnection portion) 202 that holds contact points. A plurality ofcontact points are disposed at the holding portion 202.

As the exchangeable lens 200 is mounted at the camera body 100, theholding portion 102 at which the plurality of contact points aredisposed becomes electrically and physically connected with the holdingportion 202 at which the plurality of contact points are disposed. Viathe two holding portions 102 and 202, power is supplied from the camerabody 100 to the exchangeable lens 200 and signals are exchanged betweenthe camera body 100 and the exchangeable lens 200.

An image sensor 104, such as a CMOS image sensor or a CCD image sensor,is disposed to the rear of the body-side mount unit 101 in the camerabody 100. A button 107 functioning as an input device is disposed on thetop side of the camera body 100. The user is able to issue aphotographing instruction, a photographing condition setting instructionor the like to the camera body 100 by operating an input device such asthe button 107.

FIG. 2 is a sectional view of the camera system 1 used in conjunctionwith exchangeable lenses, achieved in the first embodiment of thepresent invention. The exchangeable lens 200 includes an image formingoptical system 210 that forms a subject image. The image forming opticalsystem 210 is constituted with a plurality of lenses 210 a through 210c. The plurality of lenses 210 a through 210 c include a focusing lens210 b used when controlling the focus position for the subject image.

Inside the exchangeable lens 200, a lens-side control unit 203, whichcontrols the various units constituting the exchangeable lens 200, isdisposed. The lens-side control unit 203 is constituted with amicrocomputer, its peripheral circuits and the like (none shown). Alens-side first communication unit 217, a lens-side second communicationunit 218, a lens drive unit 212, a lens position detection unit 213, aROM 215 and a RAM 216 are connected to the lens-side control unit 203.

The lens-side first communication unit 217 and the lens-side secondcommunication unit 218 engage in data communication with the camera body100 by enabling signal exchange between the exchangeable lens 200 andthe camera body 100 via the various communication contact pointsdisposed at the holding portion 202. The lens drive unit 212, whichincludes an actuator such as a stepping motor, drives the focusing lens210 b in response to a signal input thereto. The lens position detectionunit 213 detects the position of the focusing lens 210 b by counting thenumber of pulses in a signal input to, for instance, the stepping motorat the lens drive unit 212. As an alternative, it may detect theposition of the focusing lens 210 b via a distance encoder or the likeof the known art disposed at the exchangeable lens 200.

In the ROM 215, which is a nonvolatile storage medium, specific controlprograms to be executed by the lens-side control unit 203 and the likeare stored in advance. The RAM 216, which is a volatile storage medium,is utilized by the lens-side control unit 203 as a storage area wherevarious types of data are stored.

In front of the image sensor 104, a shutter 115, via which the exposurecondition at the image sensor 104 is controlled, and an optical filter116 achieved by combining an optical low-pass filter and an infrared cutfilter are disposed. Subject light having been transmitted through theimage forming optical system 210 reaches the image sensor 104 via theshutter 115 and the filter 116.

The camera body 100 includes a built-in body-side control unit 103 thatcontrols the various units disposed at the camera body 100. Thebody-side control unit 103 is constituted with a microcomputer, a RAM,peripheral circuits and the like (none shown). A body-side firstcommunication unit 117, a body-side second communication unit 118 and alens engagement/disengagement detection unit 119 are connected to thebody-side control unit 103.

The body-side first communication unit 117 engages in data communicationwith the lens-side first communication unit 217 within the exchangeablelens 200 by exchanging signals with the lens-side first communicationunit 217 via various communication contact points disposed at theholding portion 102. Likewise, the body-side second communication unit118 engages in data communication with the lens-side secondcommunication unit 218 within the exchangeable lens 200 by exchangingsignals with the lens-side second communication unit 218 via variouscommunication contact points disposed at the holding portion 102. Thelens engagement/disengagement detection unit 119 detectsengagement/disengagement of the exchangeable lens 200 with/from thecamera body 100 based upon a signal level indicated at a specificcontact point, as will be described later, among the plurality ofcontact points disposed at the holding portion 102.

On the rear side of the camera body 100, a display device 111constituted with an LCD panel or the like is disposed. Under controlexecuted by the body-side control unit 103 for the display device 111,an image of the subject generated based upon an output from the imagesensor 104 (referred to as a through image) and various types of menuscreens via which the photographing conditions and the like can beselected are brought up on the display device 111.

Holding Portions 102 and 202

FIG. 3 shows the holding portions 102 and 202 in detail in a schematicdiagram. As shown in FIG. 3, the holding portion 102 includes 12 contactpoints BP 1 through BP 12. The holding portion 202, too, includes 12contact points LP 1 through LP 12, respectively corresponding to the 12contact points BP 1 through BP 12. In the following description, thecontact points BP 1 through BP 12 will be referred to as body-sidecontact points and the contact points LP 1 through LP 12 will bereferred to as lens-side contact points.

The body-side contact points BP 1 and BP 2 are connected to a firstpower supply circuit 120 in the camera body 100. The first power supplycircuit 120 supplies an operating voltage, with which various unitsconstituting the exchangeable lens 200, except for the lens drive unit212, are to operate, to the body-side contact point BP 1. In otherwords, when the exchangeable lens 200 is engaged with the camera body100 via the body-side mount unit 101 and the lens-side mount unit 201,the operating voltage, on which the various units (including thelens-side first communication unit 217 and the lens-side secondcommunication unit 218) in the exchangeable lens 200, except for thelens drive unit 212, are to operate, is supplied via the body-sidecontact point BP 1 and the lens-side contact point LP 1. The body-sidecontact point BP 2 is a ground terminal corresponding to the aboveoperating voltage. Namely, the body-side contact point BP 2 and thelens-side contact point LP 2 function as ground terminals correspondingto the operating voltage.

In the following description, a signal line formed with the body-sidecontact point BP 1 and the lens-side contact point LP 1 will be referredto as a signal line V33. In addition, a signal line formed with thebody-side contact point BP 2 and the lens-side contact point LP 2 willbe referred to as a signal line GND.

The body-side contact points BP 3, BP 4, BP 5 and BP 6 are used for datacommunication referred to as command data communication. These fourbody-side contact points are connected to the body-side firstcommunication unit 117. The lens-side contact points LP 3, LP 4, LP 5and LP 6 to be respectively connected to these four body-side contactpoints are connected to the lens-side first communication unit 217. Thebody-side first communication unit 117 and the lens-side firstcommunication unit 217 engage in data communication as they exchangesignals via the four body-side contact points BP 3 through BP 6 and thefour lens-side contact points LP 3 through LP 6. The data communication(command data communication) conducted by the body-side firstcommunication unit 117 and the lens-side first communication unit 217will be described in detail later.

The body-side first communication unit 117 and the lens-side firstcommunication unit 217 judge that an input signal input via a specificcontact point indicates a truth value “true” (may otherwise be referredto as 1, H, High or the like) if the signal level of the particularsignal is equal to or higher than a predetermined reference level (e.g.,2.0 v). In addition, they judge that an input signal, input from a givencontact point indicates a truth value “false” (may otherwise be referredto as 0, L, Low or the like) if the signal level of the signal is equalto or lower than a predetermined reference level (e.g., 0.8 v) set to adifferent value than the reference level mentioned above. The body-sidesecond communication unit 118 and the lens-side second communicationunit 218 make similar judgments.

In the camera body 100, the body-side contact point BP 6 is connected toa power source Vcc (e.g., 5 v) via a pull-up resistor R1. In otherwords, the body-side contact point BP 6 is pulled up. In theexchangeable lens 200, the lens-side contact point LP 6 is grounded viaa pull-down resistor R2. In other words, the lens-side contact point LP6 is pulled down.

The resistance values of the pull-up resistor R1 and the pull-downresistor R2 are selected so that a signal level corresponding to thetruth value L (e.g., a signal level equal to or lower than 0.8 v) isassumed at the body-side contact point BP 6 when the exchangeable lens200 is mounted at the camera body 100 and data communication via thelens-side first communication unit 217 is not in progress. Theresistance values may be set so that R1=10 kΩ and R2=100Ω, for instance.

If, on the other hand, the exchangeable lens 200 is not mounted at thebody-side mount unit 101, a signal level corresponding to the truthvalue H (e.g., 2.0 v or higher) is assumed at the body-side contactpoint BP 6, since the body-side contact point BP 6 is pulled up in thisstate.

The lens engagement/disengagement detection unit 119 is connected to thebody-side contact point BP 6. The lens engagement/disengagementdetection unit 119 detects engagement/disengagement of the exchangeablelens 200 based upon the signal level indicated at the body-side contactpoint BP 6. The engagement/disengagement detection executed by the lensengagement/disengagement detection unit 119 will be described in detaillater.

It is to be noted that a signal line formed with the body-side contactpoint BP 3 and the lens-side contact point LP 3 will be referred to as asignal line CLK in the following description. In addition, a signal lineformed with the body-side contact point BP 4 and the lens-side contactpoint LP 4 will be referred to as a signal line BDAT, a signal lineformed with the body-side contact point BP 5 and the lens-side contactpoint LP 5 will be referred to as a signal line LDAT and a signal lineformed with the body-side contact point BP 6 and the lens-side contactpoint LP 6 will be referred to as a signal line RDY in the followingdescription.

The body-side contact points BP 7, BP 8, BP 9 and BP 10 are used fordata communication referred to as hot line communication. These fourbody-side contact points are connected to the body-side secondcommunication units 118. The lens-side contact points LP 7, LP 8, LP 9and LP 10 respectively connected to these four body-side contact pointsare connected to the lens-side second communication unit 218. Thebody-side second communication unit 118 and the lens-side secondcommunication unit 218 engage in data communication as they exchangesignals via the four body-side contact points BP 7 through BP 10 and thefour lens-side contact points LP 7 through LP 10. The data communication(hot line communication) conducted by the body-side second communicationunit 118 and the lens-side second communication unit 218 will bedescribed in detail later.

It is to be noted that a signal line formed with the body-side contactpoint BP 7 and the lens-side contact point LP 7 will be referred to as asignal line HREQ in the following description. In addition, a signalline formed with the body-side contact point BP 8 and the lens-sidecontact point LP 8 will be referred to as the signal line HANS, a signalline formed with the body-side contact point BP 9 and the lens-sidecontact point LP 9 will be referred to as a signal line HCLK and asignal line formed with the body-side contact point BP 10 and thelens-side contact point LP 10 will be referred to as a signal line HDATin the following description.

The body-side contact points BP 11 and BP 12 are connected to a secondpower supply circuit 121 in the camera body 100. The second power supplycircuit 121 provides a drive voltage to be used to drive the lens driveunit 212 to the body-side contact point BP 12. In other words, the drivevoltage for the lens drive unit 212 is supplied via the body-sidecontact point BP 12 and the lens-side contact point LP 12. The body-sidecontact point BP 11 is a ground terminal corresponding to the abovedrive voltage. This means that the voltage assumed at the body-sidecontact point BP 11 and the lens-side contact point LP 11 is a groundvoltage corresponding to the drive voltage.

In the following description, a signal line formed with the body-sidecontact point BP 11 and the lens-side contact point LP 11 will bereferred to as a signal line PGND. In addition, a signal line formedwith the body-side contact point BP 12 and the lens-side contact pointLP 12 will be referred to as a signal line BAT.

It is to be noted that the difference between the maximum value and theminimum value taken by the electric current flowing through thebody-side contact point BP 11 and the lens-side contact point LP 11 isgreater than the difference between the maximum value and the minimumvalue taken by the electric current flowing through the body-sidecontact point BP 2 and the lens-side contact point LP 2, since the powerused at the lens drive unit 212, which includes a drive system such asan actuator, is greater than the power used in electronic circuits suchas the lens-side control unit 203 and the like in the exchangeable lens200 and no power is used in the lens drive unit 212 when the focusinglens 210 b does not need to be driven.

Command Data Communication

The lens-side first communication unit 217 engages in data communicationwith the body-side first communication unit 117 via the lens-sidecontact points LP 3 through LP 6 and the signal lines CLK, BDAT, LDATand RDY. This data communication is repeatedly executed over, forinstance, 16 ms intervals. In addition, control data transmitted fromthe body-side first communication unit 117 are received and responsedata are transmitted to the body-side first communication unit 117concurrently through this data communication. The following is adetailed description of the communication conducted by the lens-sidefirst communication unit 217 and the body-side first communication unit117.

It is to be noted that in the description of the embodiment, thecommunication between the lens-side first communication unit 217 and thebody-side first communication unit 117 will be referred to as “commanddata communication”.

FIG. 4 presents a timing chart pertaining to a specific example ofcommand data communication. When the body-side first communication unit117 and the lens-side first communication unit 217 are not engaged indata communication (prior to a time point T1 in FIG. 4), the signallevel corresponding to the truth value L is assumed at the signal lineRDY.

The body-side first communication unit 117 first verifies the signallevel at the signal line RDY at the start (T1) of the command datacommunication. The signal level at the signal line RDY indicates whetheror not communication via the lens-side first communication unit 217 isenabled. Namely, the lens-side first communication unit 217 transmits tothe lens-side contact point LP 6 a ready signal indicating whether ornot the lens-side first communication unit 217 is in a datacommunication enabled state. This ready signal is neither a data signalnor a clock signal. If the lens-side first communication unit 217 is ina data communication disabled state, a signal indicating H (High) levelis output from the lens-side contact point LP 6. As long as H level issustained at the signal line RDY, the body-side first communication unit117 does not start communication and it starts communication only whenthe signal level shifts to L level. In addition, while H level issustained at the signal line RDY, the body-side first communication unit117 does not execute the next phase of processing for communicationcurrently in progress.

Once the signal level at the signal line RDY shifts to L (Low) level,the body-side first communication unit 117 outputs a clock signal 401through the body-side contact point BP 3. The body-side firstcommunication unit 117 outputs a body-side command packet signal 402,which constitutes the first half of control data, from the body-sidecontact point BP 4 in synchronization with the clock signal 401. Inaddition, in synchronization with the clock signal 401 output to thesignal line CLK, the lens-side first communication unit 217 outputs alens-side command packet signal 403, which constitutes the first half ofresponse data, through the lens-side contact point LP 5.

Once the transmission of the lens-side command packet signal 403 iscompleted, the lens-side first communication unit 217 sets the signallevel at the signal line RDY to H level (T2). The lens-side control unit203 then starts first control processing 404 corresponding to thecontents of the body-side command packet signal 402 having beenreceived. For instance, the contents of the body-side command packetsignal 402 having been received may constitute a request for specificdata. In such a case, the lens-side control unit 203 executes processingfor generating the requested data as the first control processing 404.

Upon completing the first control processing 404, the lens-side controlunit 203 notifies the lens-side first communication unit 217 of thecompletion of the first control processing 404. In response to thenotification, the lens-side first communication unit 217 outputs anL-level signal from the lens-side contact point LP 6 (T3). In responseto this shift in the signal level, the body-side first communicationunit 117 outputs a clock signal 405 from the body-side contact point BP3. The body-side first communication unit 117 outputs a body-side datapacket signal 406, which constitutes the second half of the controldata, from the body-side contact point BP 4 synchronously with the clocksignal 405. In addition, in synchronization with the clock signal 401output to the signal line CLK, the lens-side first communication unit217 outputs a lens-side data packet signal 407, which constitutes thesecond half of the response data, through the lens-side contact point LP5.

Once the transmission of the lens-side data packet signal 407 iscompleted, the lens-side first communication unit 217 sets the signallevel at the signal line RDY to H level again (T4). The lens-sidecontrol unit 203 then starts second control processing 408 correspondingto the contents of the body-side command packet signal 402 and thebody-side data packet signal 406 having been received. For instance, thebody-side command packet signal 402 may be a drive instruction fordriving the focusing lens 210 b and the body-side data packet signal 406may indicate a drive quantity, i.e., the extent to which the focusinglens 210 b should be driven. In such a case, the lens-side control unit203 executes second control processing 408 for driving the focusing lens210 b by the extent indicated by the drive quantity.

Upon completing the second control processing 408, the lens-side controlunit 203 notifies the lens-side first communication unit 217 of thecompletion of the second control processing 408. In response to thenotification, the lens-side first communication unit 217 outputs anL-level signal from the lens-side contact point LP 6 (T5).

The communication conducted between the time point T1 and the time pointT5, as described above, constitutes a single command data communicationsession. As described above, a single body-side command packet signal402 and a single body-side data packet signal 406 are transmitted viathe body-side control unit 103 and the body-side first communicationunit 117 through a single command data communication session. Namely,while the control data are transmitted in two split parts to facilitatethe processing, the two signals, i.e., the body-side command packetsignal 402 and the body-side data packet signal 406, together constitutea set of control data.

Likewise, a single lens-side command packet signal 403 and a singlelens-side data packet signal 407 are transmitted via the lens-sidecontrol unit 203 and the lens-side first communication unit 217 througha single command data communication session. Namely, the lens-sidecommand packet signal 403 and the lens-side data packet signal 407,together constitute a set of response data.

As described above, the lens-side first communication unit 217 receivesthe control data from the body-side first communication unit 117 andtransmits the response data to the body-side first communication unit117 concurrently.

Various signals are output by the lens-side first communication unit 217and the body-side first communication unit 117 to the four signal lines(CLK, BDAT, LDAT and RDY) used for the command data communication. AsFIG. 4 clearly indicates, the signal output by the lens-side firstcommunication unit 217 to the signal line RDY undergoes the fewestsignal level shifts among these signals. This means that during commanddata communication with the camera body 100, the lens-side firstcommunication unit 217 controls the lens-side contact points LP 3through LP 6 so as to ensure that the signal level at the lens-sidecontact point LP 6 undergoes the fewest level shifts among the fourlens-side contact points LP 3 through LP 6.

It is to be noted that a predetermined time restriction (time limit)pertaining to the length of time required for the first controlprocessing 404 and the second control processing 408, is set in advancein the memory in the lens-side control unit 203, so as to avoidretarding the overall camera processing unnecessarily. The controlprocessing (task) executed on the lens-side as part of the command datacommunication is designed to be completed in approximately severalhundred microseconds to several milliseconds under normal circumstances(as long as the normal operating state is sustained on the lens-side).Accordingly, the time restriction mentioned above is set by adding sometime margin to the length of time required to complete the lens-sidetask during the command data communication. The time restriction set inthe embodiment is adjusted to an optimal value within a range of, forinstance, several tens of milliseconds to several hundreds ofmilliseconds. In other words, the lens-side control unit 203 executescontrol so as to ensure that time periods T23 and T45 in FIG. 4 do notexceed the length of time defined by the time restriction. Namely, whilethe camera body 100 is attached to the lens-side mount unit 201 (i.e.,while operation power is supplied from the camera body 100 to the lenscontrol unit 203), the lens-side first communication unit 217 controlsthe lens-side contact point LP 6 so as to ensure that the signal levelcorresponding to the truth value H is not sustained at the lens-sidecontact point LP 6 continuously over a length of time equal to orgreater than that defined by the time restriction.

Hot Line Communication

The lens-side second communication unit 218 transmits lens position datato the body-side second communication unit 118 via the lens-side contactpoints LP 7 through LP 10, i.e., via the signal lines HREQ, HANS, HCLKand HDAT. The communication conducted by the lens-side secondcommunication unit 218 and the body-side second communication unit 118is described in detail below.

It is to be noted that in the description of the embodiment, thecommunication between the lens-side second communication unit 218 andthe body-side second communication unit 118 will be referred to as “hotline communication”.

FIGS. 5A and 5B each present a timing chart pertaining to an example ofhot line communication. The body-side control unit 103 in the embodimentis configured so as to start the hot line communication over a secondpredetermined cycle Tn (e.g., over 1 ms intervals in the embodiment).This cycle is shorter than the cycle over which the command datacommunication is executed. FIG. 5A shows the hot line communicationrepeatedly executed over the predetermined cycle Tn. FIG. 5B shows a hotline communication session executed over a single communication periodTx, among hot line communication sessions executed repeatedly. Thefollowing is a description of the hot line communication procedure,given in reference to the timing chart presented in FIG. 5B.

At a start of hot line communication (T6), the body-side secondcommunication unit 118 outputs an L-level signal from the body-sidecontact point BP 7. The lens-side second communication unit 218 notifiesthe lens-side control unit 203 that the L-level signal has been input tothe lens-side contact point LP 7. In response to the notification, thelens-side control unit 203 starts executing lens position datageneration processing 501. Through the generation processing 501, thelens-side control unit 203 engages the lens position detection unit 213in detection of the position of the focusing lens 210 b and generateslens position data indicating the detection results.

As the lens-side control unit 203 completes the execution of thegeneration processing 501, the lens-side second communication unit 218outputs an L-level signal from the lens-side contact point LP 8 (T 7).As the L-level signal is input to the body-side contact point BP 8, thebody-side second communication unit 118 outputs a clock signal 502 fromthe body-side contact point BP 9. In synchronization with the clocksignal 502, the lens-side second communication unit 218 outputs a lensposition data signal 503 carrying the lens position data from thelens-side contact point LP 10.

Upon completing the transmission of the lens position data signal 503,the lens-side second communication unit 218 outputs an H-level signalfrom the lens-side contact point LP 8 (T8). In response to the signalinput to the body-side contact point BP 8, the body-side secondcommunication unit 118 outputs an H-level signal from the body-sidecontact point BP 7 (T9).

The communication conducted between the time point T6 and the time pointT9 as described above constitutes a single hot line communicationsession. As explained above, a single lens position data signal 503 istransmitted via the lens-side control unit 203 and the lens-side secondcommunication unit 218 through the single hot line communicationsession.

Signals which are neither clock signals nor data signals are output atthe lens-side contact points LP 7 and LP 8 among the four lens-sidecontact points LP 7 through LP 10 used in hot line communication. Thesignal levels at these two lens-side contact points undergo more signallevel shifts than the signal level at the lens-side contact point LP 6used in the command data communication, since hot line communication isexecuted over a shorter cycle compared to command data communication.

For instance, assuming that command data communication is executed over16 ms intervals and that hot line communication is executed over 1 msintervals, the signal level at the lens-side contact point LP 6 shiftsfour times in every 16 ms period. During hot line communication executedover 1 ms intervals, the signal levels at the lens-side contact pointsLP 7 and LP 8, which shift twice during a single communication session,each shift 32 times during each 16 ms period.

This means that during command data communication and hot linecommunication with the camera body 100, the lens-side firstcommunication unit 217 controls the lens-side contact points LP 3through LP 10 so that the lens-side contact point LP 6 undergoes thefewest signal level shifts among the lens-side contact points LP 3through LP 6.

It is to be noted that command data communication and hot linecommunication can be simultaneously executed in parallel. Namely, whileeither the lens-side first communication unit 217 or the lens-sidesecond communication unit 218 is engaged in communication with thecamera body 100, the other lens-side communication unit, too, is able tocommunicate with the camera body 100.

Exchangeable Lens Engagement/Disengagement Detection

FIG. 6A presents a timing chart showing how the lensengagement/disengagement detection unit 118 detects engagement of theexchangeable lens 200. If the exchangeable lens 200 is not mounted atthe camera body 100, the body-side contact point BP 6 remains in apulled up state (see FIG. 3) and thus, the signal level corresponding tothe truth value H is assumed at the body-side contact point BP 6. Oncethe exchangeable lens 200 is mounted, the body-side contact point BP 6assumes the signal level corresponding to the truth value L (T10) sincethe lens-side contact point LP 6 is in a pulled down state (see FIG. 3).The lens engagement/disengagement detection unit 119 detects engagementof the exchangeable lens 200 as the signal level at the body-sidecontact point BP 6 shifts to that corresponding to the truth value L asdescribed above. Upon detecting engagement of the exchangeable lens 200with the camera body 100, the body-side control unit 103 startssupplying power to the exchangeable lens 200 and also startscommunication operation to communicate with the exchangeable lens 200.

FIG. 6B is a timing chart showing how the lens engagement/disengagementdetection unit 119 detects disengagement of the exchangeable lens 200.As the exchangeable lens 200 is disengaged from the camera body 100, thebody-side contact point BP 6 resumes the signal level corresponding tothe truth value H (T11). At this point in time, the lensengagement/disengagement detection unit 119 cannot determine whetherthis signal level shift has been caused by a signal output to the signalline RDY by the lens-side first communication unit 217 or bydisengagement of the exchangeable lens 200.

Once the signal level at the body-side contact point BP 6 shifts to thatcorresponding to the truth value H, the lens engagement/disengagementunit 119 monitors the body-side contact point BP 6 to ascertain whetherthe signal level is sustained over a length of time equal to or greaterthan the length of time defined by the time restriction (described inreference to FIG. 4).

If the signal level shift having occurred at the time point T11 isattributable to a signal output by the lens-side first communicationunit 217, the body-side contact point BP 6 should resume the signallevel corresponding to the truth value L before the length of timecorresponding to the time restriction elapses following the time pointT11. However, if the body-side contact point BP 6 sustains the signallevel corresponding to the truth value H even after the length of timedefined by the time restriction elapses, the signal level shift can bedetermined to be attributable to disengagement of the exchangeable lens200. Accordingly, the lens engagement/disengagement detection unit 118detects disengagement of the exchangeable lens 200 at a time point T12occurring after a predetermined length of time T1112 equal to or greaterthan the length of time defined by the time restriction, elapsesfollowing the time point T11.

As described above, the lens engagement/disengagement detection unit 119detects disengagement of the exchangeable lens 200 if the body-sidecontact point BP 6 sustains the signal level corresponding to the truthvalue H continuously over a length of time equal to or greater than thelength of time defined by the time restriction. It is to be noted thatthe lens engagement/disengagement detection unit 119 in the embodimentdetects (judges) that the exchangeable lens has been disengaged inreference to a decision-making reference time length over which thebody-side contact point BP 6 sustains (continuously holds) the signallevel corresponding to the truth value H, “equal to or greater than thelength of time defined by the time restriction”. The length of time“equal to or greater than the length of time defined by the timerestriction” may be the exact length of time defined by the timerestriction or it may be a length of time greater than that defined bythe time restriction (up to several times that defined by the timerestriction).

It is to be noted that the signal at the body-side contact point BP 6may sustain the signal level corresponding to the truth value Hcontinuously over a length of time equal to or greater than that definedby the time restriction for a reason other than disengagement of theexchangeable lens 200 described above. For instance, the signal levelcorresponding to the truth value H may be sustained when theexchangeable lens-side is in a hung state while the exchangeable lensremains engaged with the camera body or when contact between thecommunication contact points is poor. Upon detecting that the body-sidecontact point BP 6 has sustained the signal level corresponding to thetruth value H continuously over a length of time equal to or greaterthan that defined by the time restriction for any of the reasons(causes) listed above, the body-side control unit 103 at the camera body100 executes processing for cutting off the power supply to theexchangeable lens 200.

As a result, even if the signal level at the signal line RDY on theexchangeable lens-side is continuously held at H level due to a hang orpoor contact at the communication contact points, power supply from thecamera side to the exchangeable lens-side is cut off and thus, theoperation at the lens-side control unit 203 stops, causing the lens-sidecontact point LP 6 to assume the signal level corresponding to the truthvalue L via the pull-down resistor R2. In other words, as the signallevel at the signal line RDY on the exchangeable lens-side shifts to Llevel, the camera body 100 is engaged in behavior similar to thatdescribed in reference to FIG. 6A. More specifically, the lensengagement/disengagement detection unit 119 located on the camerabody-side determines that the exchangeable lens has been reengaged andthe body-side control unit 103 starts power supply to the exchangeablelens 200 and communication with the exchangeable lens 200.

The following operational advantages are achieved in the firstembodiment of the camera system described above.

(1) The exchangeable lens 200 includes the lens-side first communicationunit 217 that engages in data communication with the camera body 100 byexchanging signals with the camera body 100 via the lens-side contactpoints LP 3 through LP 6. The lens-side contact point LP 6 is connectedto the body-side contact point BP 6 which is utilized at the camera body100 for purposes of detection of engagement/disengagement of theexchangeable lens 200. The lens-side first communication unit 217outputs a signal which is neither a data signal nor a clock signal tothe lens-side contact point LP 6 and controls the lens-side contactpoint LP 6 so as to ensure that the body-side contact point BP 6 doesnot sustain the signal level corresponding to the truth value Hcontinuously over a length of time equal to or greater than apredetermined time length while the camera body 100 is attached to thelens-side mount unit 201. Namely, the lens-side first communication unit217 controls the lens-side contact point LP 6 so as to output a signalthat disallows detection of disengagement of the exchangeable lens 200from the camera body 100 while the operating voltage is supplied fromthe camera body 100 via the lens-side contact point LP 1. This meansthat while the operating voltage is supplied from the camera body 100via the lens-side contact point LP 1, the lens-side first communicationunit 217 controls the output through the lens-side contact point LP 6 soas to ensure that the camera body 100 is not allowed to determine thatthe exchangeable lens 200 is disengaged from the camera body 100. Thelens-side contact point LP 6 is configured so that the body-side contactpoint BP 6 is allowed to assume the signal level corresponding to thetruth value L when the camera body 100 is attached to the lens-sidemount unit but no data communication is in progress via the lens-sidefirst communication unit 217. As a result, lens engagement/disengagementcan be detected without having to modify the simple communicationprocedure.

(2) At the camera body 100, the body-side first communication unit 117,which conducts data communication with the exchangeable lens 200 byexchanging signals with the exchangeable lens 200 via the body-sidecontact points BP 3 through BP 6, and the lens engagement/disengagementdetection unit 119, which detects engagement/disengagement of theexchangeable lens 200 based upon the signal level indicated at thebody-side contact point BP 6 are disposed. The body-side contact pointBP 6 is connected to the lens-side contact point LP 6, among thelens-side contact points LP 3 through LP 6, to which a signal that isneither a data signal nor a clock signal is output from the exchangeablelens 200. In addition, the body-side contact point BP 6 is configured soas to assume the signal level corresponding to the truth value H whenthe exchangeable lens 200 is not mounted at the body-side mount unit 101and to assume the signal level corresponding to the truth value L whenthe exchangeable lens is mounted at the body-side mount unit 101 but nocommunication is in progress via the body-side first communication unit117. When the exchangeable lens 200 is mounted at the body-side mountunit 101, the body-side first communication unit 117 receives, via thebody-side contact point BP 6, a signal that does not sustain the signallevel corresponding to the truth value H continuously over a length oftime equal to or greater than a predetermined time length. The lensengagement/disengagement unit 119 detects disengagement of theexchangeable lens 200 when the body-side contact point BP 6 hassustained the signal level corresponding to the truth value Hcontinuously over a length of time equal to or greater than thepredetermined time length and detects engagement of the exchangeablelens 200 when the signal level at the body-side contact point BP 6 hasshifted to that corresponding to the truth value L. As a result, lensengagement/disengagement can be detected without having to modify thesimple communication procedure.

(3) The lens-side first communication unit 217 controls the lens-sidecontact points LP 3 through LP 6 so as to ensure that the lens-sidecontact point LP 6 among the lens-side contact points LP 3 through LP 6undergoes the fewest signal level shifts during data communicationbetween the exchangeable lens 200 and the camera body 100. As a result,the circuit design pertaining to the lens-side first communication unit217 and the lens-side contact points LP 3 through LP 6 is facilitated.

(4) The exchangeable lens 200 includes the lens-side contact points LP 7through LP 10, to be respectively connected to the body-side contactpoint BP 7 through BP 10 disposed at the camera body 100 for purposes ofhot line communication, and the lens-side second communication unit 218,which engages in data communication with the camera body 100 via thelens-side contact points LP 7 through LP 10. The lens-side firstcommunication unit 217 controls the lens-side contact points LP 3through LP 6 so as to ensure that the lens-side contact point LP 6 amongthe lens-side contact points LP 3 through LP 10 undergoes the fewestsignal level shifts during data communication with the camera body 100.As a result, the circuit design pertaining to the lens-side firstcommunication unit 217 and the lens-side second communication unit 218is facilitated.

(5) The lens-side contact point LP 6 is grounded via the pull-downresistor R2 within the exchangeable lens 200. Thus, as the exchangeablelens 200 is engaged with the camera body 100, the signal level at thebody-side contact point BP 6 shifts to that corresponding to the truthvalue L, enabling engagement detection by the lensengagement/disengagement detection unit 119.

Second Embodiment

FIG. 7 is a perspective of the camera system achieved in the secondembodiment. A camera system 2 achieved in this embodiment comprises acamera body 100, a middle adapter 700 that can be detachably mounted atthe camera body 100 and an exchangeable lens 600 that can be detachablymounted at the middle adapter 700. It is to be noted that in thefollowing description, members and the like identical to those in thefirst embodiment will be assigned with the same reference numerals as inthe first embodiment, so as to preclude the necessity for a repeatedexplanation thereof.

The exchangeable lens 600 is compatible with a camera body having mountspecifications thereof different from those of the camera body 100. Inother words, a lens-side mount unit 601 of the exchangeable lens 600conforms to mount specifications different from those of a body-sidemount unit 101 at the camera body 100, and thus the exchangeable lens600 cannot be mounted at the camera body 100. In addition, while theexchangeable lens 600 is similar to the exchangeable lens 200 shown inFIG. 1 in that it includes a holding portion 602 with a plurality ofcontact points disposed thereat, located near the lens-side mount unit601, the shape of the holding portion 601 is different from that of theholding portion 102 of the camera body 100.

The middle adapter 700 is a mount adapter used to allow such anexchangeable lens 600 to be mounted at the camera body 100. Morespecifically, the casing of the middle adapter 700 is formed in acylindrical shape. The middle adapter 700 includes a first mount portion701, located at one side surface thereof, which corresponds to thebody-side mount unit 101 (conforming to mount specificationscorresponding to those of the body-side mount unit 101). The middleadapter 700 further includes a second mount portion 703, located at theopposite side surface, which corresponds to the lens-side mount unit 601(conforming to mount specifications corresponding to those of thelens-side mount unit 601). It is to be noted that the casing does notneed to be cylindrical and the embodiment may be adopted in conjunctionwith a casing assuming another shape. The first mount portion 701 can bedetachably mounted at the body-side mount unit 101 of the camera body100. In addition, the second mount portion 703 can be detachably mountedat the lens-side mount unit 601 of the exchangeable lens 600.

The middle adapter 700 includes a holding portion 702 similar to theholding portion of the exchangeable lens 200 in the first embodiment,which is provided at a position near the first mount portion 701 (on theinner circumferential side of the first mount portion 701) and projectsout along part of the inner circumference of the first mount portion 701so as to hold contact points. A plurality of contact points are disposedat the holding portion 702. As the middle adapter 700 is engaged withthe camera body 100, the holding portion 702, holding the plurality ofcontact points, becomes electrically and physically connected with theholding portion 102 with a plurality of contact points disposed thereat.Since the first mount portion 701 and the holding portion 702 adoptstructures similar to those of the lens-side mount unit 201 and theholding portion 202 having been described in reference to the firstembodiment, a further explanation is not provided.

In addition, the middle adapter 700 includes a holding portion 704,which is provided at a position near the second mount portion 703 (onthe inner circumferential side of the second mount portion 703) andprojects out along part of the inner circumference of the second mountportion 703 so as to hold contact points. A plurality of contact pointsare disposed at the holding portion 704. The exchangeable lens 600includes a holding portion 602, at which contact points are held,located near the lens-side mount unit 601. A plurality of contact pointsare disposed at the holding portion 602. As the exchangeable lens 600 isengaged with the middle adapter 700, the holding portion 602, holding aplurality of contact points, becomes electrically and physicallyconnected with the holding portion 704 with a plurality of contactpoints disposed thereat.

As engagement/disengagement of the exchangeable lens 200 is detected atthe camera body in the first embodiment, engagement/disengagement of themiddle adapter 700 is detected at the camera body 100. In other words,the individual contact points disposed at the holding portion 702 of themiddle adapter 700 are configured similar to the various contact pointsat the holding portion 202 of the interchangeable lens 200 in the firstembodiment. For instance, lens-side contact points LP 1 through LP 12,such as those described in reference to the first embodiment, aredisposed at the holding portion 702. As the middle adapter 700 ismounted, the signal level at the body-side contact point BP 6 shifts tothat corresponding to the truth value L, since the lens-side contactpoints LP 6 at the holding portion 702 is in a pulled down state. Thelens engagement/disengagement detection unit 119 detects engagement ofthe middle adapter 700 as the signal level at the body-side contactpoint BP 6 shifts to that corresponding to the truth value L, asdescribed above. Upon detecting engagement of the middle adapter 700with the camera body 100, the body-side control unit 103 startssupplying power to the middle adapter 700 and also starts communicationoperation to communicate with the middle adapter 700. The middle adapter700 functions as an intermediary to enable communication between theexchangeable lens 600 and the camera body 100 via its variouscommunication contact points located at the holding portion 704.

The middle adapter 700 further includes an adapter control unit (notshown). This adapter control unit engages in communication with thebody-side control unit 103, as does the lens-side control unit 203 inthe exchangeable lens 200 described earlier. In addition, the adaptercontrol unit executes drive control in order to drive a drive targetmember (e.g., an aperture drive lever via which aperture blades, locatedwithin the exchangeable lens 600, are driven) disposed within the middleadapter 700. Moreover, as long as the middle adapter 700 is engaged withthe camera body 100, the adapter control unit executes control similarto that executed for the signal level at the lens-side contact point LP6 of the exchangeable lens 200 as described earlier. Namely, as long asthe camera body 100 is attached to the first mount portion 701, theadapter control unit controls the contact point at the middle adaptercorresponding to the lens-side contact point LP 6 so as to ensure thatthe middle adapter contact point corresponding to the lens-side contactpoint LP 6 does not sustain the signal level corresponding to the truthvalue H continuously over a length of time equal to or greater than thatdefined by the time restriction.

As the middle adapter 700 is disengaged from the camera body 100, thesignal level at the body-side contact point BP 6 shifts back to thatcorresponding to the truth value H. If the body-side contact point BP 6sustains the signal level corresponding to the truth value H longer thanthe time length defined by the time restriction described earlier, thelens engagement/disengagement detection unit 119 detects disengagementof the middle adapter 700.

In the camera system achieved as described above in the secondembodiment, operational advantages similar to those of the firstembodiment can be achieved through the use of the middle adapter.

The following variations are also within the technical scope of thepresent invention and a single variation or a plurality of variationsmay be adopted in combination with either of the embodiments describedabove.

Variation 1

The lens-side second communication unit 218 may transmit data other thanthe lens position data to the body-side second communication unit 118through hot line communication. For instance, data pertaining to theaperture diameter or data pertaining to the blur correction lensposition may be transmitted.

Variation 2

An exchangeable lens with a manual focusing lens, in conjunction withwhich position information indicating the position of the focusing lens210 b is not required, does not need to include the lens-side contactpoints LP 7 through LP 10 and the lens-side second communication unit218. The lens engagement/disengagement detection unit 119, which detectsengagement/disengagement of the exchangeable lens 200 via the body-sidecontact point BP 6, is able to accurately detectengagement/disengagement of the exchangeable lens 200 without thelens-side contact points LP 7 through LP 10 used for hot linecommunication.

Variation 3

The present invention may be adopted in camera systems compatible withexchangeable lenses that adopt structures different from those describedin reference to the embodiments. For instance, the present invention maybe adopted in a single-lens reflex camera with a mirror disposed withinthe camera body to achieve advantages similar to those of theembodiments described earlier.

Variation 4

The middle adapter in the second embodiment may be a wide-angleconverter or a telephoto converter that includes a specific type ofoptical system. A camera system 3 in FIG. 8 represents an example of aconfiguration that includes such a middle adapter. A middle adapter 800in the camera system 3, mounted between the camera body 100 and theexchangeable lens 200 in the first embodiment, includes a third mountportion 801 corresponding to the camera body and a fourth mount portion803 corresponding to the exchangeable lens 200 and lengthens the focallength of the optical system in the exchangeable lens 200 by an extentcorresponding to a predetermined magnification factor. The presentinvention may be adopted in conjunction with this middle adapter 800.

It is to be noted that the middle adapter in FIG. 8 includes a holdingportion 802, which is connected with the holding portion 102 at thecamera body 100, located near the third mount portion 801. In addition,it includes a holding portion 804, which is connected with the holdingportion 202 at the exchangeable lens 200, located near the fourth mountportion 803. The holding portions 802 and 804 in this configuration maybe structured so that signals each input (output) via one of the contactpoints at the holding portion 802 are output (input) through thecorresponding contact points at the holding portion 804 withoutconversion. As an alternative, the microprocessor (control unit) withinthe middle adapter 800 may execute control so that, followingcommunication conducted via one of the holding portions, thecommunication results are sent through communication conducted via theother holding portion. In this case, the contact points at the holdingportion 802 should be structured similar to those at the holding portion202 in the first embodiment. For instance, the terminal used fordetection of engagement/disengagement of the middle adapter 800 shouldbe grounded via a pull-down resistor within the middle adapter 800 andthe microprocessor within the middle adapter 800 should control thisterminal as has been described in reference to the first embodiment.Furthermore, the microprocessor within the middle adapter 800 shouldcontrol the contact point at the middle adapter 800 corresponding to thelens-side contact point LP 6 so as to ensure that as long as the camerabody 100 is engaged with the third mount portion 801, the contact pointat the middle adapter 800 corresponding to the lens-side contact pointLP 6 does not sustain the signal level corresponding to the truth valueH continuously over a length of time equal to or greater than thatdefined by the time restriction explained earlier.

Variation 5

While the present invention is adopted in an exchangeable lens, a middleadapter or the like that can be detachably mounted at the camera body inthe embodiments described above, the present invention may be adopted inconjunction with an accessory other than an exchangeable lens or amiddle adapter, as long as it can be detachably mounted at the camerabody.

By adopting any of the embodiments of the present invention orvariations thereof described above, lens engagement/disengagement can bedetected through a simple structure.

The above described embodiments are examples, and various modificationscan be made without departing from the scope of the invention.

What is claimed is:
 1. A camera accessory to be detachably mounted at acamera body that includes a first body contact point and a second bodycontact point and detects disengagement of the camera accessory when thesecond body contact point sustains a signal level corresponding to afirst truth value continuously over a length of time equal to or greaterthan a predetermined time length, the camera accessory comprising: amounting device to be detachably mounted at the camera body; a firstaccessory contact point that is connected with the first body contactpoint while the camera accessory is engaged with the camera body by themounting device and to which an information communication operation withthe camera body is executed; a second accessory contact point that isconnected with the second body contact point while the camera accessoryis engaged with the camera body by the mounting device so as to allow asignal that has a level corresponding to the first truth value to beoutput to the camera body during a time period in which the informationcommunication operation via the first accessory contact point isdisallowed; and an accessory-side communication control device thatexecutes the information communication operation with the camera bodyvia the first accessory contact point, wherein: the accessory-sidecommunication control device executes control so as to ensure that atime length during which the signal that has a level corresponding tothe first truth value continues to be output at the second accessorycontact point is less than the predetermined time length while themounting device is mounted at the camera body.
 2. The camera accessoryaccording to claim 1, wherein: the camera accessory is an exchangeablelens detachably mounted at the camera body.
 3. The camera accessoryaccording to claim 1, wherein: the camera accessory is a middleaccessory that includes two mount portions; and the camera body isdetachably mounted at one mount portion among the two mount portions andan exchangeable lens, which cannot be mounted detachably at the camerabody, is detachably mounted at another mount portion among the two mountportions.
 4. The camera accessory according to claim 1, wherein apull-down resistor is electrically connected to the second accessorycontact point.
 5. The camera accessory according to claim 1, wherein theaccessory-side communication control device executes control so as toensure that a signal having a level corresponding to a second truthvalue is output at the second accessory contact point when the mountingdevice is mounted at the camera body and the information communicationoperation via the first accessory contact point is not in progress, thesecond truth value being output during a time period in which theinformation communication operation is allowed.
 6. The camera accessoryaccording to claim 1, wherein: the first accessory contact point isconnected with the first body contact point by way of a first signalline, and the accessory-side communication control device executes theinformation communication operation with the camera by shifting, on thefirst signal line, between a first level and a second level that isdifferent from the first level; the accessory-side communication controldevice executes control so as to ensure that the output at the secondaccessory contact point shifts between the signal having the levelcorresponding to the first truth value and a signal having a levelcorresponding to a second truth value, the second truth value beingoutput during a time period in which the information communicationoperation via the first accessory contact point is allowed; and duringinformation communication, the accessory-side communication controldevice executes control so as to ensure that the output at the secondaccessory contact point shifts between the signal having the levelcorresponding to the first truth value and the signal having the levelcorresponding to the second truth value less than the first signal lineshifts between its first and second levels.
 7. A camera accessory to bedetachably mounted at a camera body that includes a first body contactpoint and a second body contact point and detects disengagement of thecamera accessory when the second body contact point sustains a signallevel corresponding to a first truth value continuously over a length oftime equal to or greater than a predetermined time length, the cameraaccessory comprising: a mounting device to be detachably mounted at thecamera body; an accessory-side communication control device thatexecutes an information communication operation with the camera bodywhile the camera accessory is engaged with the camera body by themounting device; a first accessory contact point that is connected withthe first body contact point while the camera accessory is engaged withthe camera body by the mounting device so as to receive an operatingvoltage supplied from the camera body; a second accessory contact pointthat is connected with the second body contact point while the cameraaccessory is engaged with the camera body by the mounting device so asto allow a signal that has a level corresponding to the first truthvalue to be output to the camera body during a time period in which theinformation communication operation is disallowed, wherein: theaccessory-side communication control device executes control so as toensure that a time length during which the signal that has a levelcorresponding to the first truth value continues to be output at thesecond accessory contact point is less than the predetermined timelength while the operating voltage is supplied from the camera body viathe first accessory contact point.
 8. The camera accessory according toclaim 7, wherein: the camera accessory is an exchangeable lensdetachably mounted at the camera body.
 9. The camera accessory accordingto claim 7, wherein: the camera accessory is a middle accessory thatincludes two mount portions; and the camera body is detachably mountedat one mount portion among the two mount portions and an exchangeablelens, which cannot be mounted detachably at the camera body, isdetachably mounted at another mount portion among the two mountportions.
 10. The camera accessory according to claim 7, wherein apull-down resistor is electrically connected to the second accessorycontact point.
 11. The camera accessory according to claim 7, whereinthe accessory-side communication control device executes control so asto ensure that a signal having a level corresponding to a second truthvalue is output at the second accessory contact point when the mountingdevice is mounted at the camera body and the information communicationoperation is not in progress, the second truth value being output duringa time period in which the information communication operation isallowed.
 12. The camera accessory according to claim 7, wherein: theaccessory-side communication control device executes the informationcommunication operation with the camera body by way of a signal line,the information communication operation being executed by shifting, onthe signal line, between a first level and a second level that isdifferent from the first level; the accessory-side communication controldevice executes control so as to ensure that the output at the secondaccessory contact point shifts between the signal having the levelcorresponding to the first truth value and a signal having a levelcorresponding to a second truth value, the second truth value beingoutput during a time period in which the information communicationoperation is allowed; and during information communication, theaccessory-side communication control device executes control so as toensure that the output at the second accessory contact point shiftsbetween the signal having the level corresponding to the first truthvalue and the signal having the level corresponding to the second truthvalue less than the signal line shifts between its first and secondlevels.
 13. A camera accessory configured to be detachably mounted to acamera body, the camera accessory comprising: an accessory contact pointconfigured, when the camera accessory is mounted to the camera body, tooutput to the camera body a ready signal that indicates whether or notan information communication operation with the camera body is enabled,wherein the accessory contact point is configured to output, when thecamera accessory is mounted to the camera body and the informationcommunication operation is not in progress, a first level of the readysignal indicating that the information communication operation isenabled.
 14. The camera accessory according to claim 13, wherein theaccessory contact point is configured to output the first level of theready signal before the information communication operation commences.15. The camera accessory according to claim 14, wherein: the first levelis a low level of the ready signal, and a second level of the readysignal, which indicates that the information communication operation isdisabled, is a high level.
 16. A camera accessory configured to bedetachably mounted to a camera body, the camera accessory comprising: aready contact point configured, when the camera accessory is connectedthe camera body, to output to the camera body a ready signal that is ateither (i) a first level indicating that information communication isenabled or (ii) a second level indicating that the informationcommunication is disabled; a clock contact point configured, when thecamera accessory is connected the camera body and when the ready signalis at its first level, to input from the camera body a clock signal forthe information communication by way of a clock signal line, the clocksignal being input when the clock signal line is at a first level andnot being input when the clock signal line is at a second level; a firstdata contact configured, when the camera accessory is mounted to thecamera body and the ready signal is at its first level, to either outputto the camera body or input from the camera body a first data signal forthe information communication by way of a first data signal line, thefirst data signal being output or input when the first data signal lineis at a first level and not being output or input when the first datasignal line is at a second level, wherein, during an informationcommunication operation, the ready signal shifts between its first leveland its second level less than the clock signal line and the first datasignal line shift between their respective first levels and secondlevels.
 17. The camera accessory according to the claim 16, wherein: thefirst data contact is configured to output to the camera body the firstdata signal for the information communication by way of the first datasignal line; the camera accessory further comprises a second datacontact that is configured, when the camera accessory is mounted to thecamera body and the ready signal is at its first level, to input fromthe camera body a second data signal for the information communicationby way of a second data signal line, the second data signal being inputwhen the second data signal line is at a first level and not being inputwhen the second data signal line is at a second level; and during theinformation communication operation, the ready signal shifts between itsfirst level and its second level less than the clock signal line, thefirst data signal line, and the second data signal line shift betweentheir respective first levels and second levels.